You only need to have at least Leopard and iTunes 10.x. The oldest minis still support this. I have an original G4 one with a 1TB external drive that I use as my iTunes server with my iPods, iPhone 4 and iPad. Still works great. I would guess that this may be the last hurrah for the non Intel ones though. Each additional upgrade seems to be leaving the G4 further behind. I would guess an early Intel mac mini might be the best choice as it will surely be compatible for a bit longer.